<form method="post" >
姓名:<input type="text" value="admin" name="username"/>
姓名:<input type="password" value="123456" name="password"/>
年龄:<input type="text" name="age" value="18" />

<button>提交</button>
</form>
 

<?php
var_dump($_POST);
echo $_POST['username']."";
 